This invention relates to improvements in an exhaust gas purifying system, and more particularly to a technique for burning off particulate (Particulate Matter in exhaust gas, referred hereafter to as “PM”) in exhaust gas collected in a filter, by raising the temperature of exhaust gas.
In recent years, internal combustion engines, particularly diesel engines are equipped with a Diesel Particulate Filter (referred hereinafter to as “DPF”) for collecting PM in exhaust gas. When the amount of the collected PM reaches a certain level, the temperature of exhaust gas is raised to burn off PM thereby regenerating DPF, as disclosed in Japanese Patent Provisional Publication No. 2002-89327.